Solar Energy: The energy producing and saving home is very doable

This informative, helpful article, "The energy producing and saving home," is written by Ben Cuker, professor of marine and environmental science at Hampton University in Hampton, Va. His solar-powered home is on tour Oct. 1-2 for the Hampton Roads Solar Tour; admission is free, get map and directions at www.hrsolartour.com.

Background

Using fossil fuels to power our homes is not a sustainable practice. Eventually we will exhaust the world’s reserves of coal, petroleum, and natural gas. But we must act before then, as the consequences of the extraction and use of fossil fuels continue to degrade our environment. Coal and oil extraction despoil our land, and water ways, natural gas mining poisons aquifers, and the combustion of these fuels fouls our air. Carbon dioxide is a potent green-house gas that contributes to global climate change, and when it dissolves in the sea it acidifies the oceans.

What are the alternatives to fossil fuel?

Electricity produced by gravity-driven water-turning turbines (hydroelectric) is free of harmful emissions and requires no fuel, other than the solar radiation that powers the water-cycle. Yet it does damage the environment by requiring the damming of wild rivers to form reservoirs. This excludes the fish and other species that are adapted to flowing waters. The resultant flood control reduces the fertility of the river’s flood plain, by cutting off the supply of nutrient rich sediments.

Electricity from nuclear energy is the most costly to produce, as it requires very expensive facilities. Nuclear energy plants last only about 50 years and produce tons of radioactive wastes that must be managed for thousands of years. The US still lacks a designated site to store this waste; nobody really wants to live near such a place. Although the chance of catastrophic failure and release of radioactivity from a nuclear plant is small, the consequences of such an accident are huge and long lasting. Consider the ongoing impact of the Chernobyl disaster in the 1980’s.

Solar and wind energy provide two excellent sustainable alternatives. Both are intermittent, only working when either the sun shines or the wind blows. So their design application must take this into consideration. There must be a way to store the energy for later use or to network the home into a system of shared energy.

Traditional home design prior to about 1900 assumed that energy production would take place on site. Judicious placement of windows and porches provided simple passive ways of partially controlling the indoor climate. In climates requiring heating, most houses burned either wood or coal, and also used these fuels for cooking. First natural gas and then electricity became available for servicing homes in the 19th Century, and these along with heating oil replaced wood and coal. Beginning in the 1950’s air conditioning became a common feature of more affluent homes, and is considered an essential feature by today’s standards. The ready availability and cheap price of fossil fuel energy enabled builders to skip the time-tested features of natural climate control and construct designs that relied more heavily on heaters and air conditioners. So the US is glutted with poorly insulated houses that require massive energy subsidies to keep them habitable during the warm and cold months.

It is already feasible to build homes that meet all of the energy demands of their occupants. Such demonstration houses all rely on a combination of super-insulation, passive heating and cooling design elements, and active (solar and or wind) energy generation on site. While we might think that all houses should be built this way hence forth, local building-codes, don’t reflect such a reality. Moreover, it is not realistic to think that we are ready to tear-down and replace all of the millions of existing houses.

Yet the technology now exists to retrofit the present housing stock for near neutral energy demand. This requires a combination of demand reduction and onsite sustainable production.

Reducing Energy Demand

The simplest way to move toward household sustainability is to reduce the size of the energy subsidy for the house. Indoor climate control eats up the largest portion of the energy consumed by households. Measures to decrease this category include; improving insulation in attics, walls and floors, upgrading to low emisitivity windows and doors, sealing cracks and openings that permit air exchange to the outside, switching to compact fluorescent lighting that produces less heat than incandescent bulbs, tuning-up heating and cooling systems for maximum efficiency, turning down the thermostat in winter and up in summer.

The second biggest energy demand comes from hot water heaters. Traditional tank-type electric hot water heaters use more energy than gas units. First popularized in Europe, tankless or instant hot water heaters fueled by either electricity of natural gas are becoming more common. These use less energy since they only come on when the hot water faucet is opened. Traditional tanks, even if well insulated, lose most of their heat in storage mode. Taking shorter showers, washing clothes in cold water and generally avoiding wasting hot water helps conserve energy.

The next two biggest energy demands come from the refrigerator and clothes dryer. A modern high efficiency refrigerator uses half the electricity of older units.

Do we really need electric clothes dryers? Clothing dryers became popular in the 1950’s and 1960’s. Prior to then, people hung their laundry to dry on lines strung in their back yards, in basements or on porches. Today many people view laundry on the line as a “low class” act that degrades the appearance of the neighborhood, thus the practice is banned in many communities. Is such an esthetic informed by sustainability?

Lighting is next on the list for energy consumption. The new compact fluorescent bulbs use about 25% of the electricity required by traditional incandescent versions. Simply remembering to turn off the lights when not in the room also significantly reduces energy demand. Motion sensors wired to the front porch light will provided security and a welcome to evening visitors, while saving energy when the light is not needed.

Finally, kill the “energy vampires.” These are the electronic devices that use small amounts of electricity even when turned off, such as TV’s, computers, stereos, cable boxes, and gaming systems. Use power strips with switches to easily disconnect these energy vampires.

Producing Clean Energy on Site

Electricity - There are two different approaches to using wind and solar energy for the production of energy. Concentrated production relies on large scale wind farms or solar farms. Similar to traditional fossil fuel plants, this approach uses a large dedicated footprint for intensive energy production that is then distributed through the grid to our homes. Few homes offer good locations for wind generation, so such concentrated installations will be the future for electricity from wind.

The second approach is to distribute the energy producing appliances to the roof-tops and back yards of our homes. This works especially well for photovoltaic panels that produce electricity. Placed on roof-tops they occupy otherwise wasted space. The panels have the added advantage of shading the underlying sections of roof, reducing summertime heat-gain to the house. Considering the thousands of square kilometers of household rooftop, does this approach seem to make more sense than to concentrate the panels on land that could be used for farms, fields, or forests?

Using distributed solar power can be done in one of two ways. The “off-grid” approach requires storage of the electricity produced in large banks of batteries. This then provides electricity at night and on cloudy days. The most efficient way to do this is to use only DC (direct current) appliances and lighting, as this saves the loss of energy involved in converting DC to AC (alternating current). Yet finding such appliances is difficult. The “off-grid” system makes the most sense for homes located great distances from the electrical grid. Batteries are expensive and require replacement every few years.

The other approach to distributed solar electric production is the “grid-tied” system. This is the most common system installed on houses today. An inverter converts the DC produced by the photovoltaic panels (PV’s) to AC so it can be fed directly back into the electric grid. Small computers built into the inverters monitor the utility voltage and make sure that the electricity produced by the installation matches that coming from the utility. These systems use “net metering.” So when the house is using more energy than it is producing, the meter goes forward, and on a nice sunny day when the house is making more than it is using, the meter will go backwards.

How can wind be used to make electricity? The mechanical force of the wind spins the turbine blades which are connected to an electrical generator. In simple terms, the generator is comprised of an armature with magnets set inside a set of wire coils called the “field.” The spinning magnets induce a flow of electrons through the wires – producing electricity.

How can sunlight be used to make electricity? There are two basic ways to convert sunlight to electricity. One is to concentrate the light using mirrors on a liquid that when heated turns to gas. The hot gas develops high pressure that turns an electrical generator. Such systems require large scale and lack practicality at the household level.

The other approach uses photovoltaic panels in which sunlight hits semiconductors. The photons of sunlight impact electrons associated with the semiconductor, causing the electrons to flow in one direction, creating an electric current.

Thermal Energy – Since houses need so much heat for climate control and hot water, this is a good place to invest in onsite sustainable production. “Passive solar” designs allow houses to use windows and sometimes coupled with heat absorbing substances (water, ceramics, metals, and salts) to use natural radiation to best effect. These passive systems work best with a southern orientation (in Northern Hemisphere) and a low angle that approximates a perpendicular to the winter sun, which is low on the horizon. This low angel also shades the passive system from the high summer sun, reducing unwanted heat gain that time of year.

“Active solar” systems utilize a solar collector to acquire the heat from the sun, and then some sort of system to deliver that heat inside the building. These systems usually circulate a fluid, typically air or water that contains antifreeze (glycol). These active systems require electricity to power pumps to circulate the heated fluid. Effective solar collector designs capture the radiation with a black-mat finished conductor that is covered with glazing (low iron glass or plastic sheeting). The glazing permits the shortwave radiation (visible light and some ultraviolet) to enter the unit where it is intercepted by the black absorber. The flat-black finish reflects very little of the visible light and instead absorbs it and then reradiates it as long-wave radiation (heat or infrared). The glazing reflects (traps) most of this long-wave radiation back into the unit. Such solar collectors can reach temperatures as high as 395 deg F (202 deg C), and typically operate at about 212 deg F (100 deg C).

Active solar thermal systems can be mated with substances with a high specific heat (such as water and salts) that will provide short-term heat storage and help extend the effectiveness of the units after the sun goes down. Fans can circulate building air through the units to distribute the heat. But generally it is more effective to circulate a glycol-water solution through plumbing. The hot solution (hyrdronic heating) can them be circulated through radiators or piped under flooring to heat the house, or first used to heat a tank of water. These tanks are super-insulated to reduce heat-loss during storage. A heat exchanger isolates the glycol solution from the actual water in the tank if it is to be used as the house’s source of potable hot water.

Putting Solar To Work on an Old House

Solar Electric - Ben Cuker and Dawn Gerbing decided to reduce their carbon-footprint by putting solar energy to work on their old house in Hampton, VA. The original structure dates to 1939 and includes three additional rooms added in the 1970’s. When they moved into the house in 1988 it had an electric water heater and two heat-pumps for climate control. In about 1990 they replaced the electric water heater with a more efficient traditional gas unit and added a ventless gas log set to the fire place.

In order to go solar they needed to find a sunny location to place PV panels. A large maple tree grew next to the house shading the entire structure. While providing welcome relief from the summer sun, it posed a threat to the structure during large windstorms. It was removed in 2007, opening up the opportunity for harnessing solar energy on the house. However, the roof line of the original structure sloped east and west, providing no southern oriented surface for mounting the panels. The single story addition in the back of the house has a southern pitched roof, but it is shaded by the second and third stories of the original structure in the afternoon.

To get around this Ben and Dawn designed and built a “solar awning” on the south side of the house to support PV panels. This required convincing the Hampton Buildings Codes Department that the design was sound. The awning articulates, allowing adjustment to three different seasonal settings for optimal orientation. The awning also rotates down to allow painting and other maintenance on the house above it.

In April of 2009 Solar Services of Virginia Beach installed ten, 215 watt PV solar panels on the solar awning, and an inverter to convert the DC to AC. The wiring goes to the house’s circuit breaker box, through an outside emergency cut-off switch, and then to the Dominion Electric “net” meter. In its first year of operation the system produced 2,744 KWH, or 64% of the total annual usage of 4,277 KWH. During that year the system made more energy then was needed during most months of the year, but heavy demand by air conditioning in July and August, and low production in December and January accounted for the net electricity required from Dominion. In June of 2010 they had an additional ten 215 Watt panels installed on the east-facing roof of the small addition to their bedroom. This location is projected to yield only 78% of the south-facing production, but that should be enough additional electricity to meet the full electricity demand for the house.

Solar Thermal – Laundry on the Line . In 2007 Dawn and Ben quit using their electric clothes dryer. They added several clothes lines to their back porch to dry their laundry. They time their laundry activity to match sunny days as much as possible, but sometimes use small folding racks placed in warm rooms to dry cloths during spells of cloudy and wet weather.

Hot Water. In September of 2009 Solar Services installed a 4 KW solar hot water heater. The solar collector panels went on the south facing roof of the addition in the rear of the house. Although shaded in the afternoon, enough heat is collected during the day to produce 170 deg F hot water in the summer, and 120 deg F water in the winter. An electric pump circulates pressurized glycol between the solar collectors on the roof and the water storage tank in the basement. The tank includes an electrical element as a back-up for cloudy days in the winter. It is also plumbed to the old gas hot water heater as a second back up.

Hot Air. In December of 2009 Ben and Dawn designed and built a “solar heat wall” on the south- facing side of the addition on the back of the house. That addition lacks any south facing windows and was thus a natural location for this device. It is 8 feet tall and twenty feet wide. It is constructed as a 4-layer sandwich. The outside is a polycarbonate glazing, with a one-inch gap above flat-black aluminum flashing. Behind the aluminum flashing is another one-inch gap for circulating the heated air. A system of baffles channels the airflow up and down 10 two-foot wide chambers. Behind this is foil-faced half inch foam insulation board that is mounted on half inch sheets of plywood, screwed to the house. An AC fan blows cool air from the room into the heat wall through a small conduit at the bottom of the first baffle chamber, and it returns as heated air (90 – 160 deg F) to the room via a conduit at the bottom of the last baffle chamber. An automatic snap-switch mounted in the heat wall turns the fan on at a temp. of 120 deg. F, and off when it drops to 90 deg. F. On sunny days it typically runs from about 9:45 AM to about 3:15 PM.

Solar Attic Ventilation. In June of 2010 Ben installed two small solar panels on the west facing main-house roof to power two 12 volt fans for ventilating the attic. These fans were designed as after-market units for cooling automobile engines. They were originally installed to run the solar heat wall, but proved insufficient and repurposed as attic ventilators.

Economics of going solar. The PV system cost $36,000 to install. But a 30% Federal tax credit brought down the true cost of the system to $21,600. The electricity produced by the system is sold on the SREC (Solar Renewable Energy Credit) market for $200 a megawatt (MW). This market was created to allow utilities meet their obligations for obtaining required amounts of energy from renewable sources. The current system should produce about 5 MW per year, yielding about a $1,000 return in SREC income. Since the house will create all of its own electricity on an annual basis, it will save about $600 that would go to Dominion (the company still collects about $96 per year for connection charges and tax). The system should pay for itself in about 13.5 years, and after

The solar hot water system cost $6,800. The federal tax credit reduced the real price to $4,760, and a special Virginia program to stimulate green industry provided an additional $4000 credit. So in the end the solar hot water system cost only $760 to install. We also sell the thermal energy SREC’s produced by that system, yielding $400 per year. Considering the $200 that used to be spent on gas each year to make hot water, the solar system has already paid for itself. In addition, Ben and Dawn now discontinue gas service from May – October. This saves the $20 per month minimum charge (6 x $20 = $120 per year), and it only costs $15 for reconnection.

Questions (cite sources and show calculations for each answer)

1. What is the average electrical energy consumption per household in the US, in France, and in Virginia?

2. What percent of the electricity produced in the US comes from: coal, oil, natural gas, nuclear, hydroelectric, solar, and wind (report a percentage for each source)? What is the mix for Virginia?

3. Some states require a certain percentage of the energy distributed by utilities to come from renewable sources. Compare the states of Virginia and California in this regard and provide the specifics.

4. How many single household dwellings are occupied in Virginia (census data may help)? Suppose that half of these were suitable for installing a 4 KW PV system like that on Ben and Dawn’s house. How much energy would that generate each year? What portion would that be of the electricity used each year in Virginia?

5. For the typical US household, what portion of their energy budget (watts, not dollars) is spent on; heating, cooling, hot water production, refrigeration, lighting, clothes drying, and electronics? Provide the break-down for each item.

6. How do community association rules and restrictive covenants influence the ability of homeowners to add solar features to their houses? Provide actual some examples.

An excellent resource is found at: http://www.ucsusa.org/clean_energy/clean_energy_101/